1. Field of the Invention
The present invention relates to systems and methods for generating electricity from solar radiation, and in particular, to a method and apparatus for notch filtering for triple junction solar cells.
2. Description of the Related Art
Solar panels are typically used to generate power in spacecraft. These solar panels comprise a plurality of solar cells typically arranged in a planar matrix of multiple layers. Solar cell current is produced by photons causing electrons to jump energy states within solar cell junctions.
Increasing a solar cell's absorption of incident solar energy increases the solar energy available for the solar cell to convert into electricity. However, it can also increase the temperature of the solar cell, and solar cells operate with reduced efficiency (η) at elevated temperatures.
Early technology solar cells (including those using double junction or silicon technology) respond to relatively limited wavelength bands of solar energy, and often used reflection filters to reflect some of the solar energy at unneeded wavelengths to reduce their temperatures.
Newer technology solar cells include three or more junctions. Such solar cells are discussed in U.S. Pat. No. 6,380,601, issued to Ermer et al and “1-eV GaInAs Solar Cells for Ultrahigh-Efficiency Multijunction Devices” by D. J. Friedman, J. F. Geisz, S. R. Kurtz, and J. M. Olson, published July 1998 and Presented at the 2nd World Conference and Exhibition on Photovoltaic Solar Energy Conversion, 34% Efficient InGaP/GaAs/GaSb Cell-Interconnected Circuits for Line-Focus Concentrator Arrays,” Munich Conference, 2001, by L. M. Fraas et al., all of which are hereby incorporated by reference.
Unfortunately, filters designed for two junction solar cells are inappropriate for use with triple junction cells because the solar cells respond to a wider wavelength band than are passed by those filters. What is needed is a filter design that maximizes the current output of solar cells with three or more junctions. The present invention satisfies that need.